The present disclosure relates to an image processing apparatus and method, and more particularly, to an image processing apparatus and method capable of improving the image quality of a decoded image.
With the high quality of images, high dynamic range (HDR) images that have a large number of gray scales per pixel have recently been spread. At present, the HDR images are applied to estimation of visual characteristics, examination of an outer appearance, or the like. In the future, the HDR images are thus expected to be applied also to fields of in-vehicle cameras, monitoring cameras, medical images, astronomical images, and the like. However, since the HDR images have a large number of gray scales per pixel, the data sizes of the HDR images are larger than those of dynamic range images according to the related art. For example, a recording load or a transmission load is larger. For this reason, compression and decompression technologies (encoding and decoding technologies) become more important when HDR images are processed than when the dynamic range images according to the related art are processed.
Several types of encoding (compression) methods for the HDR images have been suggested. For example, a method of compressing a range using a preprocessing function in a non-linear manner and performing encoding such as JPEG has been suggested (for example, see “High-Dynamic-Range Still Image Encoding in JPEG2000” by R. Xu, S. N. Pattanaik, and C. E. Hughes, IEEE Computer Graphics and Applications, vol. 25, no. 6, pp. 57 to 64, 2005). According to this method, the preprocessing function can be first applied to the entire HDR image in consideration of visual characteristics, and thus a luminance range in which the sensitivity of a human visual system (HVS) is low is compressed. In addition, linear quantization is performed to encode (compress) the image finally in conformity with the JPEG2000 scheme. Since this method is performed on the assumption of irreversible compression, this method has a superior performance to many HDR image compression methods.